iPhone or iPad can't find the AirPrint printer
Start with the Wi-Fi. An AirPrint printer can be working normally and still stay hidden if the phone/tablet and printer are on different networks.
1. Check the iPhone or iPad Wi-Fi
Open Settings → Wi-Fi and note the network with the checkmark.
2. Check the printer Wi-Fi
If the printer has a screen, look at its Wi-Fi or Network screen. The network name should normally match the iPhone/iPad.
If one device is on Guest or Visitor Wi-Fi, move it to the normal home or office network if you can.
3. Restart the printer normally
Turn the printer off, wait a few seconds, then turn it back on. Wait until it is ready before checking the printer list again.
4. Try AirPrint from a simple app
Open Photos, Mail, or Safari, tap Share or Actions, then Print. Tap Printer and see whether the printer appears.
5. Check whether the exact printer supports AirPrint
If it still does not appear, check the printer maker's information or Apple's AirPrint printer list for the exact model. AirPrint itself does not require a separate iPhone/iPad driver.